Duplex radio transmitter



July 14, 1936. J EVANS 2,047,622

DUPLEX RADIO TRANSMITTER I Filed Aug. 11, 1934 \r m H g Q N N a m E a 5QI' 3 L2 1 7'0 MODULATOR INVEN'I'OR John Evans a'r'romvgy Patented July14, 1936 UNIT ATNT it:

DUPLEX RADHO TRANSMITTER John Evans, Riverside,

N. 3., assignor, by mesne Application August 11,

5 Claims.

This invention relates to duplex radio transmitters and moreparticularly to a device embodying means to facilitate the changing overof resonant networks so that the transmitter may be employed on eitherone of two frequency bands, one band being in the ultrahigh frequencyrange and the other of relatively low frequency.

An object of my invention is to provide a duplex radio transmitter inwhich either of two frequency bands may be selected to the exclusion ofthe other, and when so selected, the transmitter may be operated withoutappreciabie loss of energy.

It is known that for transmission of an ultrahigh frequency carrierwave, a push-pull arrangement of the oscillator tubes and of theamplifier tubes provides the optimum conditions of operation. On theother hand, when low frequencies are to be transmitted, the symmetricalcircuits which are provided, may best be operated in parallel. V

In order that the tubes and certain portions of the oscillator andamplifier networks of my invention may be selectively adapted to operateeither at ultrahigh frequency or at the lower frequency, I have providedcertain simple switching arrangements and circuit connections which canbe handled with a minimum of effort.

The objects and advantages of my invention will best be understood uponreference to the following detailed description when read in connectionwith the accompanying drawing in which the sole figure thereofrepresents a circuit dia-- gram of a preferred embodiment.

Referring to the drawing, I show a pair of electron discharge devices Iwhich may either be ordinary triodes or tubes of any other suitabletype. The cathodes 2 of these tubes have been shown as of the indirectlyheated type. Directly heated filament cathodes may be used instead, ifpreferred. The grids 3 are connected to a resonant loop 4, the tuning ofwhich may be accomplished by means of variable capacitors 5. The loop 4cooperates with the tubes I to operate the same in a push-pull manner togenerate an ultrahigh frequency. The output circuit for these tubes isalso made resonant by means of the inductive loop 6 and the tuningcondensers l. Anode potential is supplied to the plates of the tubes Ifrom any suitable source as indicated by the plus and minus signs at 8.The output energy of the oscillator may be transferred through thecoupling condensers 9 to a resonant input network including the grids ofa pair of electron discharge tubes Ill. The tuning of the input circuitfor the tubes may be adjusted to a desired value as by 1934, Serial No.739,436

means of the inductances l. The output circuits of the tubes Ill mayalso be tuned as by means of the inductive loop I2 and the tuningcondensers I3.

The tubes IE and the circuit connections thereto constitute one stage ofamplification. A second stage of amplification, like the first, may alsobe provided, constituting the tubes M. The output energy from theamplifier tubes i l may be inductively transferred to a work-circuitincluding the inductive loop l5 and the adjustable capacitors iii. Ifdesired, one of the capacitors it may be connected to a short-waveantenna and the other to a counterpoise. If, however, it

is desired to employ a dipole antenna, then the condensers It may beconnected thereto in any suitable manner well understood by thoseskilled in the art.

The oscillator with its two stages of amplification, as hereinbeforedescribed, may be supplemented by additional tuned circuits foroccasional use so as to enable the transmitter to operate at acomparatively low frequency. The additional networks comprise, in theoscillator stage, a tuned tank circuit having an inductance I? and avariable capacitor l8; and, for each of the two stages of amplification,a tank circuit comprising an inductance l9 and variable capacitor 2%.When these tank circuits are connected into the oscillator-amplifiernetwork, the various pairs of electron discharge tubes are caused tooperate in parallel. For the low frequency operation, the inductiveloops 4, 6, l2 and l 5 provide paths of negligible inductive value. Thevalues of the condensers 5, 1 and I3 are such that they offer a highimpedance to low frequency currents. It will be seen, therefore, thatfor all practical purposes, the resonant networks, which are providedfor the ultrahigh frequency service, may be ignored when connecting inthe tank circuits for use in low frequency transmission.

By a simple switching operation, the various pairs of electron dischargetubes may be operated either push-pull or in parallel. For this purposeI provide preferably a relay 2!, the operating circuit for which mayinclude a battery 22 and the push-button switch 23-24. By depressing thepush-button 24, the relay becomes energized so as to open theshort-circuiting contacts 25 and 26 and also to close pairs of contacts21, thus grounding two tuning condensers 28. The character of thisswitching operation is such that the tank circuits, includinginductances I1 and I9 and tuning condensers l8 and 20, may be operablyplaced in circuit with the oscillator and amplifier tubes therebycausing these tubes to operate in a parallel manner. The grounding ofthe condensers 28, each on one side thereof, completes the arrangementfor making the oscillator circuit resonate at the desired low frequency.

When it is desired to operate my transmitter at low frequency I employ atank circuit 33 connected with the output circuit from the tubes [4through the loop l2. The output from a modulator may be impressed uponthis tank circuit 33. Coupled to the inductance 29 of the tank circuitis a coil 30 on which the modulated output energy may be impressed. Thiscoil 30 is in circuit with a variable inductance 3i having a connectionto a low frequency antenna. Neutralizing condensers 32 are providedbetween stages of the low frequency tank circuits of the amplifierstages.

From the foregoing description the advantages of my simple switchingarrangement will readily be seen. The transmitter, at times, may beoperated at ultrahigh frequency when the pushbutton 24 is not depressed.The conditions then obtained provide for push-pull operation of thevarious pairs of electron discharge tubes. At other times, thetransmitter may be operated at a comparatively low frequency bydepressing the push-button 24 and providing for the introduction intothe operable portion of the transmitter network of the several lowfrequency tank circuits. If desired, the switching arrangements may bemanually operated instead of operating the same by means of the relay2|.

Although I have described a preferred embodiment of my invention, itwill be readily understood by those skilled in the art thatmodifications may be made without departing from the spirit thereof. Iintend, therefore, that no limitations shall be imposed except as areneces sitated by the prior art and by the scope of the appended claims.

I claim as my invention:

1. In a radio transmitter, an ultra-high frequency oscillator andamplifier having tuned input and output circuits and tuned interstagecoupling impedances, a pair of electron discharge tubes connected forpush-pull operation in the oscillation generator stage, other pairs ofelectron discharge tubes likewise connected in the amplifier stages, aset of relatively low frequency tank-circuits and additional reactancesat times cooperable with said discharge tubes for generating andamplifying relatively low frequency oscillations, means for at suchtimes causing respective pairs of said tubes to operate in parallel, andmeans for short-circuiting at least two of said tank circuits and fordisabling said additional reactances when said transmitter is t oberendered operable at an ultra-high frequency.

2. Apparatus in accordance with claim 1 characterized in that saidshort-circuiting and disabling means is relay operated.

3. In combination, a plurality of sets of electron discharge tubesarranged in stage-by-stage pairs for the generation and amplification ofradio frequency oscillations, an ultra-high frequency oscillator networkinto which the first pair of said tubes is connected, amplifier networksinto which succeeding pairs of tubes are connected, means for energizingsaid tubes in a push-pull manner and for controlling the operation ofsaid networks for at times producing a modulated ultra-high frequencysignal, and means including additional resonant circuits connectiblestage-by-stage to said pairs of tubes for producing a relativelylow-frequency signal therein, the last said means being operable furtherto cause the respective tubes of each pair to. function in parallel.

4. A device in accordance with claim 3 having a relay-controlled switchfor rendering the last said means operable.

5. In a duplex radio system, a generating and amplifying networkcomprising a plurality of electron tubes, circuit means connecting saidtubes at one time in push-pull relation and at another time inparallel-feed relation, tuning means permanently connected in saidnetwork and adapted to render the same resonant at an ultra-highfrequency when said tubes are in pushpull relation, second tuning meansfor rendering said network resonant to a relatively lower frequency andadapted to be connected into said network only when said tubes are inparallelfeed relation, said first mentioned tuning means being sopermanently connected in said network as to produce negligibleelectrical efiect when said tubes are in parallel-feed relation, and.switching means for shifting said network from one frequency to theother.

JOHN EVANS.

